1. Field of the Invention
The present invention relates generally to electrostatic particle or droplet injectors, and more particularly to an apparatus and related method for injecting dielectric particles or droplets by first charging the dielectric particles or droplets using ultraviolet light induced photoelectrons, and then ejecting the charged particles or droplets by utilizing an electrostatic force.
2. Description of Background Information
Charged droplet atomizers are well known in the art, and have been used for a wide variety of applications. Commonly, such atomizers use electrostatic force to form an atomized field of small droplets, which droplets are preferably of relatively uniform size. This technique involves the use of a high voltage to electrostatically atomize the fluid into small droplets.
Two typical examples of such electrostatic atomizers are found in U.S. Pat Nos. 4,255,777, to Kelly, and in 4,748,043, to Seaver et al. The Kelly patent induces a free excess charge on fluid contained within a housing chamber using at least two electrodes. The fluid containing the free excess charge is supplied to a spray mechanism, and is accelerated outwardly into small droplets by a strong electrostatic field generated by a ground electrode. The droplets are accelerated toward the ground electrode, and pass through one or more apertures in the ground electrode.
The Seaver et al. patent uses a first electric field between a plurality of needles and a plate, with the needles being disposed concentrically with respect to holes in the plate to cause a mist of highly charged droplets to be emitted from the needles. A second electric field is used to draw the droplets to the surface of an object to be coated with a thin but uniform coating. Both the Kelly patent and the Seaver et al. patent thus use an electrostatic atomizer to generate a mist of droplets.
The point which needs to be made is that both of these references are limited to the use of generating a mist of conductive droplets for the desired purpose. If the liquid is not conductive, the atomizers will not work. Similarly, it would not be possible using conventional electrostatic techniques to inject particles, unless the particles are made of a conductive material.
In most situations, the use of particles or droplets which are made of a conductive material has not presented a problem. However, recently a problem occurred which made it desirable to be able to inject particles made of nonconductive dielectric material. A brief description of the nature of the problem encountered is helpful to the understanding of the necessity of a dielectric particle injector.
During the Magellan mission to Venus, a number of anomalous events were observed in the use of the star scanner. The star scanner is a light sensitive device used to calibrate the attitude control system of the spacecraft. The events involved the detection of false incidences in which the star scanner indicated the detection of a star when in fact no star was in a position to be detected.
After a number of other possible causes for the false incidences were identified and ruled out, the possibility of particulates released from the surface of the spacecraft reflecting sunlight into the star scanner was indicated as the most likely possibility. The outer surface of the spacecraft was astroquartz, and it was suspected that these particles were the cause of the false incidences detected by the star scanner. It was hypothesized that the particles were released from the astroquartz surface of the spacecraft due to thermal shock when the astroquartz was exposed to the sunlight.
In order to confirm the theories advanced as to the cause of the star scanner anomalies, it was necessary to run several experiments in which dielectric particles were charged and released by a particle injector device.
Accordingly, it is the primary objective of the present invention that it provide an apparatus and a method for injecting dielectric particles in a manner analogous to conventional particle injection of conductive droplets and particles.
Thus, it is an objective of the present invention that a charge must initially be placed on the dielectric particles or droplets in order to provide a manner of controlling the ensuing movement of the dielectric particles or droplets. Appropriate apparatus and a suitable method must be developed to accomplish this objective.
It is a further objective that the appropriately charged dielectric particles or droplets be ejected into a desired area using an electrostatic force. The charged dielectric particles or droplets may then be maintained in the desired area through electrostatic confinement.
It is a still further objective of the present invention that the dielectric particles or droplets may be charged either negatively or positively by varying the charging technique. It is another objective of the present invention that the apparatus used be relatively compact and inexpensive, both to construct, as well as to operate and maintain. Finally, it is also an objective that all of the aforesaid advantages and objectives of the present invention be achieved without incurring any substantial relative disadvantage.